The present invention relates to a process for producing fiber aggregate, and more particularly, it relates to a process for producing fiber aggregate in which most fibers are about one-dimensionally oriented. "One-dimensionally oriented" means that many fibers are oriented in substantially the same direction. This definition is applied not only to the fiber aggregate but also to the orientation step mentioned later. Surface active agents promote fiber orientation in the dielectric liquid.
Heretofore, fiber aggregate of short fibers or whiskers has been produced in the following means.
A centrifugal forming method which employs a centrifugal forming apparatus as shown in FIG. 8 (Japanese Patent Laid-open No. 65200/1985). According to this method, an aqueous suspension of silicon carbide whiskers or the like is fed through the supply pipe 24 to the porous cylindrical vessel 23 which is lined with the filtration film 25 and disposed in the outer cylinder 21. The hollow fiber aggregate 26 is formed by centrifugal action. Water is discharged from the outlet 22.
Another conventional method which employs a suction forming apparatus as shown in FIG. 9. According to this method, a prescribed amount of fiber-containing fluid 34 is fed to the cylinder 31, and a pressure is applied to the fluid 34 by the plunger 32 arranged above the cylinder 31. At the same time, the filtrate is removed by vacuum suction through the filter 33 disposed at the bottom of the cylinder 31. Thus the fibers in the fluid are oriented and aggregate.
Other conventional methods include the papermaking method and spraying method.
The fiber aggregate formed by the centrifugal method or suction method is not composed of one-dimensionally oriented fibers, but is composed mainly of two or three-dimensionally oriented fibers. The fiber aggregate with such orientation has a disadvantage that it does not provide a sufficient strength in the desired one-dimensional direction when incorporated into fiber-reinforced metal (referred to as FRM hereinafter). Additional disadvantages are the low volume ratio of fiber and the excessive spring back at the time of compression molding.
According to the conventional method, it was impossible to produce one-dimensionally oriented fiber aggregate and it was only possible to produce two or three dimensionally oriented fiber aggregate.